1. Field of the Invention
The present invention relates to a method and apparatus for the treatment of poultry with gas before slaughter in order to anaesthetize or kill the poultry, in which gas containing oxygen and carbon dioxide is used.
2. Description of Related Art
The use of poultry meat is increasing continuously, and there is an increasing focus on the ethical aspects of such production. It is normal to anaesthetize the animals directly before slaughter for several reasons, but mainly in order that the animals shall behave calmly and do not feel pain or discomfort during the slaughter process. Today, anaesthetization is mainly carried out electrically, a method which has many problematic aspects. Increased focus on these aspects has led poultry producers to look for new, better alternatives for anaesthetization/slaughter.
Traditional anaesthetization is currently carried out by lifting the poultry out of a transport crate and suspending them individually in a shackle. Here they are suspended by the legs with the head down. This is in itself a major stress factor which causes the animals to become agitated. The animals remain suspended like this, often for several minutes, while they are conveyed to a plant for electrical anaesthetization. The anaesthetization itself takes place by each individual animal passing through a salt bath with an electrical charge. The head is lowered into the bath and the body serves as a living conductor between the current carrying salt bath and the shackle. This often leads to haemorrhaging in the thighs and breast muscles, broken legs on account of severe convulsions and consequently poor meat quality is obtained.
After the electrical anaesthetization, the animals are slaughtered individually by cutting their necks. This is also important in order to obtain immediate bleeding. The anaesthetization is important to ensure that the animals do not feel pain when their necks are cut. U.S. Pat. No. 4,107,818 discloses an apparatus for slaughtering small animals using carbon dioxide gas. The apparatus comprises two chambers, where the first chamber contains carbon dioxide gas which, together with oxygen, is intended to render a gentle anaesthetization of the animals. The concentration of carbon dioxide in the first chamber should be over 40%, while the concentration of oxygen should not be more than 50%. Such a large proportion of oxygen is desired to avoid stress and discomfort by the animals. At the same time, it is desirable to use a relatively high concentration of carbon dioxide in order to produce a rapid anaesthetic reaction by the animals, which may be adult cats. Mainly pure carbon dioxide gas is used in the second chamber, which causes the death of the animals when they are placed in this chamber.
WO 94/15469 discloses a method and apparatus for anaesthetizing poultry in which anaesthetic gas is used in two stages or chambers. A first stage comprises, as in the previous reference, an anaesthetic gas containing oxygen. The concentration of oxygen must be at least 15% and anaesthetic gases such as carbon dioxide, nitrous oxides, ether, etc. can be used. A preferred concentration of gas in this first stage is 60 vol. % carbon dioxide and 30 vol. % oxygen. As in the previous reference, the second stage must also comprise an anaesthetic gas. A mechanical conveyor system comprising shackles or cages can be used to convey the poultry through the chambers.
Other methods of anaesthetization include the use of gas with a low oxygen content (anoxic anaesthetization) in which the anaesthetic gas may also comprise a mixture of nitrogen or argon together with CO.sub.2. An example of such a technique is disclosed in U.S. Pat. No. 5,152,714.
Commonly, the above mentioned methods all start the treatment directly at a high concentration of carbon dioxide, without paying much attention to the animals and how they react upon the treatment. According to the experience of the applicant, this may cause the following problems when treating poultry:
1. The poultry will feel pain in the mouth and throat region, because of the high concentration of carbon dioxide. PA1 2. When treating for instance turkeys, the period needed to treat these animals may vary between each individual, because some of the turkeys may stop breathing in the actual atmosphere. Before breathing the stunning gas, some of them rather consume the oxygen contained in their internal air sacks.